Standard PET bottle polymer typically has an intrinsic viscosity, or IV in the range of 0.76 to 0.84 dl/g. Copolymer modification (acid or glycol) has been used to decrease the crystallization rate and widen the injection molding processing window. Standard PET bottle polymers with copolymer modification typically have between 0% and 6% IPA modification, or 0% and 3% CHDM modification in order to reduce the crystallization rate and allow the production of clear preforms weighing up to 100 grams.
Processing equipment and technology have been developed to produce stretch blow molded bottles weighing up to 800 grams specifically for the bulk delivered bottled water market. The use of stretch blow molding technology provides advantages in production output and bottle thread finish quality. However, this equipment has been limited to the use of amorphous resins, such as polycarbonate, in order to maintain the desired clarity in the preforms and bottles.
The use of a crystallizable polyester, such as PET, in a stretch blow molded application can give important advantages when compared to the use of an amorphous polymer. Specifically, the crystallizable polyester can be oriented, or mechanically stretched to give dramatically improved mechanical properties and crack resistance at reduced bottle weight. Using standard PET bottle polymer formulations in these large containers, however, results in the either the formation of crystalline haze in the thicker areas of the bottle, or a very narrow processing window during the production of the preforms and bottles.